Bio-inspired self-shaping ceramics

Abstract

Shaping ceramics into complex and intricate geometries using cost-effective processes is desirable in many applications but still remains an open challenge. Inspired by plant seed dispersal units that self-fold on differential swelling, we demonstrate that self-shaping can be implemented in ceramics by programming the material's microstructure to undergo local anisotropic shrinkage during heat treatment. Such microstructural design is achieved by magnetically aligning functionalized ceramic platelets in a liquid ceramic suspension, subsequently consolidated through an established enzyme-catalysed reaction. By fabricating alumina compacts exhibiting bio-inspired bilayer architectures, we achieve deliberate control over shape change during the sintering step. Bending, twisting or combinations of these two basic movements can be successfully programmed to obtain a myriad of complex shapes. The simplicity and the universality of such a bottom-up shaping method makes it attractive for applications that would benefit from low-waste ceramic fabrication, temperature-resistant interlocking structures or unusual geometries not accessible using conventional top–down manufacturing.

Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

“…(A) Magnetic field required for alignment as a function of the size of Al 2 O 3 platelets coated with superparamagnetic iron oxide nanoparticles ( SPION s) . (B) Setup typically utilized to apply a rotating magnetic field to a suspension of responsive anisotropic particles . (C) Threshold frequency required to align disk‐shaped particles within the plane of an external rotating magnetic field.…”

“…(D) Alignment factor extracted from optical microscopy images indicating the typical timescales required for the orientation of Al 2 O 3 platelets under an external magnetic field . (E) Microstructure of a green body containing Al 2 O 3 platelets oriented in a specific direction within a matrix of Al 2 O 3 nanoparticles . (F) Sintered microstructure of a ceramic bilayer containing grains aligned in specific orientations in each of the layers …”

“…(E) Microstructure of a green body containing Al 2 O 3 platelets oriented in a specific direction within a matrix of Al 2 O 3 nanoparticles . (F) Sintered microstructure of a ceramic bilayer containing grains aligned in specific orientations in each of the layers …”

“…The use of external fields to control the microstructure of ceramic parts enables unique alignment configurations beyond what can been typically achieved using the shear forces often applied in ceramic manufacturing processes like tape casting and extrusion. In the example depicted in Figure D, Al 2 O 3 platelets were magnetically aligned within a suspension of Al 2 O 3 nanoparticles, which was eventually consolidated into a green body through DCC . Using the aligned platelets as seeds for templated grain growth, dense ceramic microstructures with distinct programmable local texture can be achieved.…”

“…(B) Self‐shaping ceramics that undergo programmable bending during sintering. The width of the ceramic bilayer increases from left to right . (C) Chiral seedpod that twists upon drying and the reinforcement architecture leading to the shape change .…”